Using Current Logged User on Query

Hello all,
I’m new to Grafana and i’m trying to do something.

I’ve a dashboard the show several statistics of several databases.
The user access for each database is on a MySQL table.

I with to query the MySQL table (i already create the datasource) using something like:

select db_name from db_user_access where username = $USERNAME

My problem is on $USERNAME variable.
Is there any option to get the current logged username to use on this query?

Best regards